This invention relates to the fabrication of free standing objects utilizing thermal spraying technology and more particularly to the formation of works of art and other objects in which a material is melted and then caused to be sprayed onto a preformed screen-like substrate.
Thermal spraying is generally described as any process in which a material, usually a metal or alloy, is caused to be melted and then with the aid or air or other gas is propelled to the surface of a substrate where the melted metal solidifies to provide a coating on the substrate which provides a benefit to the substrate.
Common uses of thermal spraying include providing corrosion resistant coating on steel in automotive applications, providing abrasion resistance on high impact tool parts, providing hardness to turbine blades for the aircraft industry, providing dimensional control of critical parts, repairing of defective or worn parts and/or to enhance the electrical characteristics of a substrate.
In the century since the invention of thermal spraying, several similar but different methods have been widely used. These methods include the following:
1. Combustion Wire Spray—in which fuel gas such as acetylene, natural gas, hydrogen, propane, stabilized methylacetylene propadiene or other fuel and an oxygen source, burning at about 3,000 degrees Centigrade, are used to melt a wire composed of the material to be deposited which is then forced by compressed air through a nozzle and then deposited on a substrate. The material of the substrate is not critical except to the extent that the properties of the coated substrate need to meet the requirements of the intended application.
2. Combustion Powder Spray—in which a powered coating material is supplied to the gaseous combustion mixture instead of a wire. The use of a powder provides additional flexibility in the choice of coating materials. For example, aluminum oxides or ceramic materials may be used.
3. Electric Arc Wire Spray—in which two wires across which an electric arc is struck to provide the energy to melt the wire coating material which is then propelled to the surface of the substrate, as in the above processes. This process has the advantage of not requiring the use of fuel/oxygen gases.
4. High Velocity Oxygen Fuel Spray (HVOP)—in which a high velocity gas such as nitrogen is used to propel the coating powder into a cone-shaped flame where the coating material can be fully or partially melted resulting in a much more controlled deposition of the coating material.
5. Plasma Spray—in which a gaseous plasma is formed which can reach temperatures of 6,600 to 16,600 degrees Centigrade which can melt any coating material. Thus, this process has the ability to utilize the widest choice of coating materials. Local cooling of the substrate enables the temperature of the substrate to remain between 38 to 260 degrees Centigrade enabling virtually any material to be used depending on the application.
6. Chamber Controlled Atmosphere Thermal Spray—in this method the thermal spray process is carried out in a chamber in which all aspects of the environment can be controlled allowing the deposited coating can be more accurately controlled. For example, the thickness of coatings deposited in the first five methods is in the range of 0.5 to 2.5 mm; this process enables the thickness to range 0.05 to greater than 10 mm.